Lagan Valley MP, Mr Jeffrey Donaldson, may this week decide whether to resign from the Ulster Unionist Party and either join the DUP or align himself with the party in a less formal anti-Belfast Agreement bloc.
Mr Donaldson told The Irish Times last night that he could not support either Mr David Trimble's leadership or his policy, and that he would not be acceding to the UUP executive's demand that he toe the party line.
He was in the middle of a consultation process with like-minded anti-agreement unionists and while it was unlikely that he would make a decision today he might finally decide on his political future later in the week, he added.
While the logic of Mr Donaldson's refusal to accept party policy is that he would leave the UUP, he stressed that he had not yet taken a final decision.
He conceded, however, that there was little point in taking the issue to another meeting of the Ulster Unionist Council, which again indicates that Mr Donaldson has reached the point of no return.
DUP sources appear confident that Mr Donaldson will apply to join their party.
His fellow MPs, the Rev Martin Smyth and Mr David Burnside, who with him resigned the party whip at Westminster because of their opposition to the joint declaration, seem unlikely to resign from the UUP.
New Ulster Unionist MLAs Ms Arlene Foster and Ms Norah Beare are, however, considering resigning from the party if Mr Donaldson takes the initiative. If all three joined the DUP, the DUP would then have six seats at Westminster compared to five for the UUP, with two of them - Mr Smyth and Mr Burnside - refusing the party whip.
It would also leave the DUP with 33 Assembly seats with the UUP reduced from 27 to 24 - a factor that would strengthen the DUP's hand in the new year review of the Belfast Agreement.
Ms Foster could not be contacted for comment last night but Ms Beare, an MLA in Mr Donaldson's Lagan Valley constituency, said she had not finally decided on what she would do. She would consult with Mr Donaldson before making up her mind. "If he leaves I will probably follow," she said.
She was adamant, however, that like Mr Donaldson she would not support Mr Trimble or the policies he was pursuing. "If Jeffrey can't accept the policies, then I certainly can't," she added.
Ms Beare said she was strongly opposed to the Hillsborough joint declaration, particularly the annex that ensured that the "on the runs" would not serve any time in prison and, as she viewed it, would get an effective amnesty for their crimes.
Her nephew was John Graham who, with fellow RUC officer David Johnston, was murdered by the IRA in Lurgan in 1997, and she could not accept that their killers could be effectively exonerated for their deeds.